Apparatus for coating the interiors of hollow bodies

ABSTRACT

Apparatus for coating the interior cylindrical surface of objects such as metal cans for food, beverages and other substances which need protection against injurious reaction with or pollution from contact with the material of the can. Airless spray coating of such surfaces revolving at high speed by stationary spray nozzles external of the can. The nozzles project impinging airless sprays having desirable patterns through respective ends of open ended can cylinders into longitudinally elongated contact with the interior surface.

United States Patent 1191 Hogstrom 5] Mar. 19, 1974 APPARATUS FOR COATING THE $147,004 4/1966 Dosser 117/18 INTERIORS 0 HOLLOW BODIES 2,895,449 7/1959 Oldfield, Jr. 118/306 3,413,955 12/1968 Patti 1 113/55 Inventor: d in F- fl gs r m, North 2,619,430 11/1952 Fink 117/35 Olmstead, Ohio 2,620,284 12/1952 MacWilliam 117/94 4 [73] Ass1gnee: Nordson Corporation, Amherest, Z 8 8 819 8/1958 Schoenfeld Jr 34/21 Ohio Primary Examiner-Mervin Stein [22] Filed: Nov. 26, 1971 Assistant Examiner-Leo Millstein Attorney, Agent, or Firm-Bosworth, Sessions, & 121] App]. No.. 202,465 McCoy Related US. Application Data [621 Division ofSer, No. 16,733, March 5, 1970, Pat. No. [57] ABSTRACT 3,640,758. Apparatus for coating the interior cylindrical surface of objects such as metal cans for food, beverages and [52] US. Cl 118/316, 1 17/96, 1 l7/lO5.4, other substances which need protection against injuri- 118/317, 118/318, 118/320 ous reaction with or pollution from contact with the [51] Int. Cl B05b 7/08 material of the can. Airless spray coating of such sur- [58] Field of Search 117/96, 97, 105.4; 118/55, faces revolving at high speed by stationary spray noz- 1 18/302, 306, 315, 316, 317, 318, 320 zles external of the can. The nozzles project impinging airless sprays having desirable patterns through re- [56] References Cited spective ends of open ended can cylinders into longi- TE STATES PATENTS tudinally elongated contact with the interior surface.

3/1963 Walter 239/246 10 Claims, 9 Drawing, Figures Pmmznm 19 m4 331979456 SHEET 1 OF 3 Baal PAIENIEDIAR \9 I974 3 797' 456 sum 2 OF 3 7 1 APPARATUS FOR COATING THE INTERIORS OF HOLLOW BODIES This is a division, of application Ser. No. l6,733 filed March 5, 1970, now U.S. Pat. No. 3,640,758.

BACKGROUND OF THE INVENTION This invention relates to apparatus for coating the interiors of cylindrical objects such as metal cans and more particularly, to improved apparatus for applying a uniform coating to the interior surface of a cylindrical container while both ends are open.

Various means have been proposed for coating the interiors of cans used to contain food, beverages and various liquids or gases to protect the contents from contact with the can material. These means have varied to some extent depending upon the characteristics of the can to be coated. The prior practices described below and our own invention are directed particularly to coating circular cylindrical cans.

A commonly produced type of metal can is madein three pieces. Three-piece cans, so called, comprise open ended cylindrical body shells with separate top and bottom end discs which may be coated separately and apart from the body shell. Theinterior of the cylindrical can body is conventionally made of metal and has a seam running the length of the can. This seam may be of any common type such as a lapped seam which is soldered and crimped or cemented, or a butt seam which is welded.

Spray coating the interior of the double open end can, or cylinder, has generally been accomplished in the prior art by an air atomizing or airless spray nozzle mounted on a lance that is reciprocated into and out of the can along its axis while the can is rotated. In the lancing operation the spray may be turned on either while the lance carrying the nozzle is reciprocated from its innermost position to a position outside the can, while moving from an external position to the inside of the can, or during reciprocation both into and out of the can.

Several difficulties are encountered with the use of the lancing operation. The coating material tends to be applied to the wall of the can in a helical path which often results in helical streaks along the can wall. Other problems occur in timing the spray with the movement of .the lance. In particular, it is difficult to cut off the flow of coating material at the precise instant that the spray begins to be projected outside the open end of the can as the lance emerges therefrom, and at the same time supply a sufficiently thick coating to the can wall adjacent the open end. Overspray is always excessive and, consequently, maintenance of the reciprocating device and the related mechanism is required at frequent intervals. Finally, the lancing method is quite inefficient in that considerable time is required to move the lance into the can and to withdraw it therefrom.

Another system for coating the interiors of double open end cans is illustrated in Eberhart U.S. Pat. No. 2,189,783. The Eberhart patent teaches the employment of two air spray nozzles for alternately spraying the interior of a can while it is rotating. Each can to be sprayed is indexed to a spraying station where it is rapidly rotated in a particulardirection while a spray of liquid coating material is projected against the interior surface through one open end.Excess spray which is blown through the can body is carried away by an exhaust pipe located adjacent the opposite end of the can.

The excess spray is drawn off into the exhaust pipe by an exhaust fan or blower. The overspray loss is wasteful and burdensome.

After several revolutions of the can the spray is'automatically cut off and the can is conveyed to another spraying station where it is revolved rapidly in the opposite direction. The interior of the can is sprayed with the liquid coating material through the opposite end of the can while the can is revolved. The can is thus sprayed from opposite ends alternately while being revolved in opposite directions. The can is then conveyed away from the last spraying station and dropped onto an inclined discharge runway which carried it to a suitable place of disposal.

The system disclosed by Eberhart is inefficient in that two spraying operations are required to adequately coat the interior of the can. Moreover, the system of Eberhart as well as those described above is quite wasteful of coating material in permitting a high percentage of overspraying which not only results in wasted coating material but also necessitates the expenditure of a large amount of time for cleaning of equipment. 7

SUMMARY OF THE INVENTION face. A more particular object is to provide apparatus for spraying the interiors of double open end cans including two fixed airless spray nozzles positioned at opposite ends of a rotating can, the overlapping spray from the nozzles uniformly coating the interior surface of the can. A l A preferred form of apparatus according to the present invention includes means'for rotating the object about its own axis, a first spray nozzle positioned adjacent one open end of the object, and a second spray nozzle positioned adjacent the other open end of the object. The nozzles are oriented to spray coating material through opposite open ends of the rotating object into angular longitudinally elongated contact with the interior thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a plan view of apparatus for spraying the interiors of can bodies through both open ends according to this invention.

FIG. 2 is a fragmentary side view of can rotating means suitable for use in this invention.

FIG. 3 is a plan view of a conventional drumhead nozzle illustrating particularly the nozzle orifice.

FIG. 4 is a plan view of a controlled distribution" nozzle illustrating particularly the nozzle orifice.

FIG. 5 shows the distribution pattern of a conventional drumhead spray nozzle, preferred for use in this invention.

FIG. 6 shows the distribution'pattern of a controlled distribution spray nozzle.

FIG. 7 is a plan view of two conventional drumhead nozzles spray coating the interior of a can in accordance with a preferred form of this invention.

FIG. 8 is a sectional view taken along the line 8-8 of FIG. 7.

FIG. 9 is a plan view of two controlled distribution nozzles spray coating the interior of a can in accordance with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A. Coating Apparatus The cans or other hollow bodies to be coated must be indexed one by one to a spraying station where they are revolved rapidly to be sprayed by stationary airless spray guns. The cans, still rotating, are then dropped or stepped out of the indexing apparatus to an inclined belt or chute on which they continue to rotate and roll to a baking oven. The belt and/or chute is of such a length that the cans will roll for a sufficient time and sufficient revolutions to allow the coating to become tacky enough so that it will no longer flow. The uniformity of coating obtained during spraying is thus not impaired before the coating is fixed by baking. The cans are then moved into the oven where the coating is baked at a prescribed temperature for a proper time.

Suitable can indexing and rotating apparatus for our purposes is disclosed in US. Pat. No. 2,189,783 to Eberhart. The apparatus shown there may be employed for indexing and rotating cans. Our method and apparatus for coating the interiors of cans requires, however, only one spraying station and one direction of rotation for the cans to be sprayed instead of two stations where cans are rotated in opposite directions as taught by Eberhart.

Preferably, the spraying of the can interiors should result in a uniform film distribution with a weight of coating of a particular number of milligrams per square inch according to manufacturers specifications. Coating materials may be vinyl, epoxy, butoxy, phenalic, acrylic, alkyd, modifications of the above, or other suitable coatings.

Film distribution is commonly determined electrically by measuring the resistance of the film at a plurality of points on the interior surface of the can. Overspray may be ascertained by determining the weight gain of the can and the weight of oversprayed material which is captured during the spraying process. Overspray is then calculated as a percentage of the weight of material sprayed on the can plus the weight of the captured over-spray material. 1

In FIGS. 1 through 6 preferred forms of apparatus for coating the interiors of hollow bodies such as cans is illustrated.

In FIG. 1 can indexing and rotating apparatus, generally designated A, is shown rotating a double open end can shell 10 at a spraying station S where two fixed, preferably like or similar, nozzles 12 and 13 are positioned at opposite ends of the can to spray and coat the interior thereof. The nozzles 12 and 13 are oriented with respect to the axis of the can, its direction or rotation and the intended line and angle of contact of the spray fan with the inside of the can to provide the very rapid coating of uniform thickness discussed more fullybelow. The nozzles 12, 13 and the automatic guns 12g and 13g therefor are rotatably, pivotally and adjustably mounted on indexing tables 15, 15 respectively, that allow each nozzle to be positioned bodily and rotated about horizontal and vertical axes with respect to the interior of the can to be coated.

Each can is rotated in a direction that advances the exposed edge of the lapped joint of the shell of the can foremost into a spray fan. The nozzles may be oriented to direct a tangential component of the spray fan at the leading edge of the lapped joint. The can is rotated at high speed, characteristically between 500 and 3,000 revolutions per minute, with a typical example being 1,800 rpm. The coating material is sprayed into the interior of the can during a little more than three revolutions, e. g. for about 100 to 200 milliseconds. A uniform coating of desired thickness, for example, 3.5 to 6.5 milligrams per square inch is deposited. Overspray is minimized by selecting and/or adjusting the angle of incidence between the coating material and the interior surface of the can to overlap the sprays and, preferably, to produce mutual impingement and interference between oppositely directed sprayed particles or streams. The coating material must have properties of good wetability and adhesion, and viscosity is characteristically within a range of 14 to 40 seconds as measured with a Zahn No.2 efflu x cup at 77 Flhecoating is deliber- V ately sprayed off the proximate edge of the can for a distance of, for example 1/16 inch to ensure full coating thickness to and on the edge.

Immediately after each can is coated and while still rotating it is stepped to a releasing station generally indicated as 16, FIG. 1, where it is released from the rotating and indexing apparatus and caused to roll down an inclined chute 18 to and/or into a baking oven 20. By causing the freshly coated can to continue to rotate for 30 to seconds at about 270 rpm and/or roll down the chute 18 at the same rate for the same time the coating material is prevented from accumulating in the can, and is caused to set with uniform thickness before baking. The length of the inclined chute 18 is such that the can is caused to make a minimum number of setting revolutions, fifty for example, during which the paint becomes tacky so that it will not flow, and volatiles have some chance to escape the can before entering the baking oven. At the end ofinclined chute 18 the can may enter the oven 20 where the paint is baked at a prescribed temperature; e.g. at 300 F for about 6 minutes, sufficient to cure and harden the applied film of the particular coating material.

While we have mentioned our preference for particular speeds of rotation of typical cans while the coating spray is being applied, we also prefer that the can be rotated no less than a whole revolution, obviously, and also that the can be rotated a whole number of revolutions plus a fraction of a revolution corresponding to the circumferential distance the can rotates while the flow from the nozzle builds up from zero to full-flow, and vice versa, i.e., while the valve in the paint gun is moving from closed to open, and vice versa. With a solenoid actuated, pneumatically operated valve the time taken for valve opening and closing is small but finite, and long enough to permit the rapidly moving coated surface to move an appreciable distance and be covered with a circumferential wedge of coating material of increasing depth while the valve is opening, and, desirably, should be covered with an equal and opposite wedge of decreasing depth while the valve is closing. Our teaching is essentially to effect the overlap as fully as practicable as examination of a few trial runs will suggest. It will also occur to those skilled in the art that imperfection or omission of the overlap will diminish in importance as the number of painting revolutions and coatings increase beyond the first one.

FIG. 2 illustrates suitable means for rotating a can at the spraying station S in FIG. 1. As shown in FIG. 2 the cans to be sprayed areheld within a turret 21 which rotates incrementally about its axis to present the cans to the rotating means, generally designated'R. The rotating means includes a driven roller 22 supported by a bracket 23 secured to a frame. An idling roller 24 maintains the can in firm frictional engagement with the driven roller.

Rotation of the driven roller is effected by a series of meshing gears 22, 25 and 26 driven by a sprocket 27 which in turn is driven by a chain 28. The chain meshes with a driving sprocket (not shown). After receiving its coating each can is indexed to the releasing station 16 and rolls down the chute 18 as described above. The can rotating apparatus shown in FIG. 2 is illustrated and described in detail in the Eberhart patent discussed above. Our invention, however, requires only one spraying station and one set of can rotating apparatus instead of the two stations and sets of can rotating apparatus required by Eberhart.

A preferred form of spray nozzle for use in our invention is shown in FIG. 3 and is commonly known as a drumhead nozzle. A common method of gaging the distribution of flow from a particular nozzle is to spray a short burst of coating material against a vertical substrate with the spray pattern oriented with its long axis horizontal. Typically the substrate contains alternating lands and grooves to offset the effect of adverse influr ences such as the blast from the spray gun which can cause wash out or distortion of the true spray pattern. Therefore, the quantity of coating material sprayed on any particular area will be reflected by the length, longer or shorter, of the rivulet in the groove running vertically downward from beneath it.

characteristically aparticular nozzlewill reflect its own peculiar characteristics when gaged by the above described method. A drumhead. nozzle, preferred for use in our method, has the spray pattern F shown in FIG. 5, skewed heavily toward one end, in ideally, a 100 percentpercent flow distribution but, practically, in a substantially 95 percent percent flow distribution. The maximum flow of coating material occurs at a point 31 approximately 95 percent of the distance'from one end of the fan and 5 percent from the other end. The amount of material flowing in the rest of the fan tapers substantially linearly from the point of maximum flow to points of minimum flow at each end of the can. i

The drumheacl nozzle B shown in FIG. 3 has an orifice 0 that is widest at one end 32 to produce the point of maximum output 31 in the fan F and tapers to a narrowest point33 corresponding to the point of minimum output in the spray fan.

Another form of nozzle which can effectively be used in our invention is the controlled distribution" nozzle, the spray pattern of which is shownin FIG. 6. As shown in FIG. 6, the maximum flow of coating material occurs at a point 31' approximately 75 percent from one end of the fan F and 25 percent from the other end. The amount of material flowing in the rest of the fan tapers substantially linearly from the point of maximum flow 31, to points of minimum flow at each end of the fan.

An illustrative form of orifice 0 for a controlled distribution nozzle B to give a -25 distribution pattern is shown in FIG. 4. This nozzle may correspond substantially to the familiar V-notch nozzle in which the orifice is slashed through a substantially hemispherical dome d with a single cut to give a well known symmetrical pattern, except that the orifice o" is a smooth merger of a long narrow cut from the left, as viewed, with a short wide cut from the right giving maximum width to the orifice at about the 75 percent 25 percent line k to produce the 75-25 spray pattern shown in FIG. 6. This nozzle is disclosed and claimed in application of Stumphauzer, Hogstrom, Nord, Schneider and Rood and assigned to the assignee of this application Ser. No. 261,027 which is a division of application Ser. No. 13,598 filed Feb. 24, 1970.

B. Coating Can Bodies with two Open Ends FIGS. 1, 7 and 8 illustrate diagrammatically the practice of our invention with a pair of conventional drumhead nozzles 12 and 13, having axes 12a and l3a, to coat the interiors of double open end cans 10. The nozzles are positioned similarly at opposite ends of the can and to the same side of the axis of the can body, FIG. 7, and have their axes 12a and 13a inclined at an angle i, FIGS. 1 and 7, measured horizontally with respect to the vertical plane v through the axis of the can body. The nozzles arepreferably inclined to direct the spray fan F parallel to the horizontal plane 11, FIG. 8, and are positioned a distance 2 from the plane of the can opening as shown in FIG. 7. The horizontal and vertical distances of the nozzles from the intersection of planes h and v are represented by x and y, respectively in FIG. 8.

The drumhead nozzles 12 and 13 are so positioned that the 5 percent or narrow portions N of the fans overlap and, preferably, impinge upon each other over their entire width while the percent or wide portions W ofthe fans are overlapped by, for example, one inch and, preferably, impinge upon each other over that distance. The can 10 is rotated in the direction indicated by the arrow a, FIG. 8, so that the leading edge of the seam 34 is rotated directly into the spray fan F to be directly and completely coated thereby.

A beneficial effect of the impinging sprays is the reduction and substantial elimination of overspray. Our tests and present observations suggest that although the portion of the can beneaththe overlapped part of the spray, FIG. 7, would apparently get more than its share of paint, such is not the actual result in terms of milligrams per square inch deposited in the middle as compared with the deposit elsewhere in the can. The nonoverlapping portions of the spray fans provide uniform, minimum,desired coatings on the flanges 35 and 36 of can 10 and produce the same uniform coating over the adjacent areas of the can interior. The tapered distribution patterns of the nozzles with the areas of greater output directed farther into the can compensate for the different distances from each nozzle to the parts to be coated. The result is a uniform coating over all areas of the can interior.

We have found that under some: conditions of paint wetability, viscosity, etc., and rapid rotation of the can while simultaneously spraying impinging spray fans into both ends of the can body, there tends to be produced a coating of lesser thickness on the portion of the can beneath the impinging portion of the'fans. We presently suspect this to'be caused by, possibly centrifugal force, possibly an excess of volatile solvents momentarily confined in the material on and near the middle of the can and/or by the formation of a pressure wall" in a center section of the can from which a surprising quantity of the coating particles rebound.

The pressure wall" is presently believed or suspected to be built up from pressure injected into the can interior by the impinging spray fans, rapid release of solvents from the fans, and the rotation of the can. We have found that the effect of the pressure wall can be overcome by overlapping and impinging the portions of the two fan sprays adjacent their points of maximum output 31 as described above so that a greater volume of coating material is directed to the impinging areas.

Where the controlled distribution nozzles, FIG. 4, producing the pattern shown in FIG. 6, are employed they should be positioned so that the 25 percent or narrow portions N of the fans are aimed farthest inwardly and completely overlap and, preferably, impinge upon each other while the wide or 75 percent portions W of the two spray patterns overlap and, preferably, impinge partially.

As shown in FIG. 9 the controlled distribution nozzles 12, 13 are positioned with respect to the can to be coated essentially the same as the drumhead nozzles with the 25 percent portion N of each pattern being directed farthest inwardly. The portions N of the two patterns impinge upon each other over their entire width while the portions W impinge over a part of their width. The non-impinging areas of the portions W provide a uniform coating over the remainder of the can interior of substantially the same thickness as that beneath' the impinging areas of the sprays.

As with the drumhead nozzles, the greater volume of material in the impinging portions of the fans appears to overcome the suspected effect of the pressure wall. The controlled distribution nozzles, also, when employed in our invention for coating the interiors of double open end cans, produce a substantially uniform coating over the can interior with substantially reduced overspray,'regard also being bad for spraying conditions such as thewetability of the-coating, its viscosity,

etc.

Whether drumhead nozzles, controlled distribution nozzles or other nozzles are employed to practice our invention we prefer that the two sprays be directed into aligned opposition and mutual impingement as described above. The cans are coated satisfactorily, however, if the two sprays are slightly misaligned so that they overlap but do not impinge.

For an example according to our invention for spraying the double open end can 10 with drumhead nozzles, they were positioned at an angle i of 52 with respect to the plane v. The can 10 was about 2 11/16 inches in diameter and 4 13/16 inches long. The nozzles flowed 0.12 gals/minute of water at 500 psi. In this example the coating was sprayed at 750 psi. The distance 2 from the nozzle to the plane of the can opening, FIG. 7, was about inches. The distance x from the nozzle to the intersection of planes v and h was about 1.25 inches and the distance y, FIG. 8, was zero inches. The can was rotated at 1,650 rpm and the spray from the nozzles was turned on for 135 milliseconds. The coating material was a vinyl lacquer reduced to a viscosity of 20 seconds as measured with a Zahn No. 2 cup at 77 F. The reducing vehicle was a suitable solvent such as MIBK (methyl-isobutyl-ketone) and xylene. The mate rial washeated to a temperature of 135 [40 F. After spraying and coating the can was released from its painting station and continued to be rotated and rolled at about 272 rpm for 3060 seconds before delivery to the baking oven. In the oven the can was baked for about 6 minutes at a temperature of 300 F. The baked and cooled coating was uniform within a maximum variation of 1.25 milligrams per square inch and overspray was within 4 percent.

For an example according to our invention for spraying the double open end can 10 with controlled distribution nozzles 12 and 13', they were positioned at an angle 1' of 55 with respect to the plane v. The can 10 was about 2 Il/l6 inches in diameter and 4 13/16 inches long. The nozzles 12' and 13 flowed about cc/minute of water at 40 psi. In this example the coating was sprayed at 750 psi. The distance 2 from the nozzles to the plane of the can openings, FIGS. 7 and 9, was about inches. The distance x from the nozzle to the intersection of planes v and h was about 1.25 inches and the distance y, FIG. 8, was 0 inches. The can was rotated at 1,650 rpm and the spray from the nozzles was turned on for milliseconds. The can was then post rolled at 272 rpm for 60 seconds. The coating material was a vinyl lacquer reduced to a viscosity of 22 seconds as measured with a Zahn No. 2 cup at 77 F. The reducing agent was a suitable solvent such as MIBK (methyLisobutyl-ketone) and xylene. In the oven the can was baked for about 6 minutes at a temperature of 300 F. The baked and cooled coating was uniform within a maximum variation of 1.25 milligrams per square inch and overspray was less than 4 percent.

While we have specifically illustrated and described a preferred and an alternate form of our invention, changes and improvements will occur to those skilled in the art who come to understand its essential principles and accomplishments. We do not therefore wish to be confined to the specific forms of our invention herein specifically disclosed, nor in any other way inconsistent with the progress by which our invention has promoted the art.

What we claim is:

1. Apparatus for coating the interior surface of a cylindrical object having open ends comprising, in combination, means for rotating said object about its own axis, a first airless spray nozzle positioned adjacent a first open end of said rotating object, a second airless spray nozzle positioned adjacent a second open end of said rotating object, said first and second spray nozzles being oriented so that their axes are disposed at angles to the rotational axis of the object to direct their sprays of coating material simultaneously through opposite open ends of the object, the angular orientation of each nozzle being such that the spray from each nozzle falls short of the open end of the object which is disposed remote from the respective nozzle from which the spray is projected.

2. The apparatus as defined in claim 1 wherein said first and second spray nozzles are provided with orifices that produce flat, fan shaped spray patterns.

3. The apparatus as defined in claim 1 further comprising means connected to said rotating means for causing said object to roll about its own axis to allow said coating material to partially dry.

4. The apparatus as defined in claim 3 further comprising an oven connected to said rolling means for receiving said object and applying heat thereto to allow the coating material to solidify.

5. The apparatus of claim 1 in which said spray projecting means directs said spray from said pair of nozzles into mutual impingement.

6. Apparatus for coating the interior surface of a cylindrical object having open ends comprising, in combination, means for rotating said object about its own axis, a first spray nozzle positioned adjacent a first open end of said rotating object, a second spray nozzle positioned adjacent a second open end of said rotating object, said first and second spray nozzles being oriented to spray coating material through opposite open ends of said rotating object into angular longitudinally elongated contact with the interior thereof and being oriented so that the sprays therefrom are directed into aligned opposition and mutual impingement.

7. Apparatus for coating the interior surface of a cylindrical object having open ends comprising, in combination, means for rotating said object about its own axis, a first spray nozzle positioned adjacent a first open end of said rotating object, a second spray nozzle positioned adjacent a second open end of said rotating object, said first and second spray nozzles being oriented to spray coating material through opposite open ends of said rotating object into angular longitudinally elongated contact with the interior thereof, said first and second spray nozzles being provided with orifices that produce flat fan-shaped spray patterns which are skewed so that the point of maximum output in each pattern is adjacent one end of the fan.

8. The apparatus as defined in claim 7 wherein said first and second spray nozzles are positioned so that the point of maximum output in each spray pattern is nearer the end of the object remote from the nozzle providing the pattern.

9. The apparatus as defined in claim 8 wherein said spray patterns overlap and impinge over' a portion of the width of eachpattern adjacent the point of maximum output.

10. The apparatus as defined in claim 9 wherein said first and second spray nozzles are drumhead nozzles.

UNITED STATES PATENT OFFICE A 1 CERTIFICATE OF CORRECTION a Patent No 3,797,456 Dated March 19, 1974 Inventor-(s) Edwin q trom It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

At 731 Assigneefl' correct the spelling of Amherst-.

Column 3, line 31 delete "method and".

Column 3', line 63 after "direction" change "or" to -of--. Column 5, 54 change "can" to -fan-.

Signed and sealed this 9th "day ofJuly 1974.

(SEAL) Attest: V

MCCOY M GIBSON ,1 JR. c. MARSHALL DANN Attesting Officer Commissioner of Patents roan ra-wsono-ss) 

1. Apparatus for coating the interior surface of a cylindrical object having open ends comprising, in combination, means for rotating said object about its own axis, a first airless spray nozzle positioned adjacent a first open end of said rotating object, a second airless spray nozzle positioned adjacent a second open end of said rotating object, said first and second spray nozzles being oriented so that their axes are disposed at angles to the rotational axis of the object to direct their sprays of coating material simultaneously through opposite open ends of the object, the angular orientation of each nozzle being such that the spray from each nozzle falls short of the open end of the object which is disposed remote from the respective nozzle from which the spray is projected.
 2. The apparatus as defined in claim 1 wherein said first and second spray nozzles are provided with orifices that produce flat, fan shaped spray patterns.
 3. The apparatus as defined in claim 1 further comprising means connected to said rotating means for causing said object to roll about its own axis to allow said coating material to partially dry.
 4. The apparatus as defined in claim 3 further comprising an oven connected to said rolling means for receiving said object and applying heat thereto to allow the coating material to solidify.
 5. The apparatus of claim 1 in which said spray projecting means directs said spray from said pair of nozzles into mutual impingement.
 6. Apparatus for coating the interior surface of a cylindrical object having open ends comprising, in combination, means for rotating said object about its own axis, a first spray nozzle positioned adjacent a first open end of said rotating object, a second spray nozzle positioned adjacent a second open end of said rotating object, said first and second spray nozzles being oriented to spray coating material through opposite open ends of said rotating object into angular longitudinally elongated contact with the interior thereof and being oriented so that the sprays therefrom are directed into aligned opposition and mutual impingement.
 7. Apparatus for coating the interior surface of a cylindrical object having open ends comprising, in combination, means for rotating said object about its own axis, a first spray nozzle positioned adjacent a first open end of said rotating object, a second spray nozzle positioned adjacent a second open end of said rotating object, said first and second spray nozzles being oriented to spray coating material through opposite open ends of said rotating object into angular longitudinally elongated contact with the interior thereof, said first and second spray nozzles being provided with orifices that produce flat fan-shaped spray patterns which are skewed so that the point of maximum output in each pattern is adjacent one end of the fan.
 8. The apparatus as defined in claim 7 wherein said first and second spray nozzles are positioned so that the point of maximum output in each spray pattern is nearer the end of the object remote from the nozzle providing the pattern.
 9. The apparatus as defined in claim 8 wherein said spray patterns overlap and impinge over a portion of the width of each pattern adjacent the point of maximum output.
 10. The apparatus as defined in claim 9 wherein said first and second spray nozzles are drumhead nozzles. 